Process and apparatus for heat exchange between two currents of gas



March 20, N34, E. ALTENKlRCH PROCESS AND APPARATUS FOR HEAT EXCHANGE BETWEEN TWO CURRENTS OF GAS Filed Nov. 27. 1929 2 Sheets-Sheet 1 I: trlilllrlllllbllln fm/enfor targ; if

March 1934. .E ALTE NKII QCH Q 1,951,336

PROCESS AND APPARATUS FOR HEAT EXCHANGE BETWEEN TWO CURRENTS OF GAS Filed Nov. 27. 1929 2 Sheets-Sheet 2 Patented Mar. 20,1934

PROCESS AND APPARATUS FOR HEAT EX- CHANGE BETWEEN TWO CURRENTS OF GAS Edmund Altenkirch, Neuenhagen, near Berlin, Germany, assignor, by mesne assignments, to

The Hoover Company, North Canton, Ohio, a

Corporation of Ohio Application November 27, 1929, Serial No. 410,020 In Germany November 30, 1928 9 Claims.

My invention relates to improvements in the process and apparatus for exchanging heat between two currents of gas. Q

It is well known in the art to bring warm and cold currents of gas into heat exchange relation with each other by conducting them in counterflow through pipes located side by side or within each other and forming a heat exchange device. This known apparatus enables a good exchange of heat only when no vapors capable of being condensed exist in the gases. If such vapors are admixed with the gases, the latent heat which the condensable vapors carried along by the hotter gas current give up during their condensation or liquefaction cannot be utilized.

The object of my invention is to provide a process and an apparatus by means of which this drawback may be eliminated. I attain the end in view by utilizing the heat set free by the condensation of the vapors contained in the gas current to be cooled to cause the evaporation of a corresponding quantity of liquid within the gas current to'be heated. Also by means of my improved process, the content of condensable vapor increases in the gas current to be heated. This is particularly useful in absorption machines with an admixed inert gas. v v

The process according to my invention is particularly simple if no separate liquid is used for the evaporation in the gas current to be heated, but the condensate of the vapors carried along by the gas current to be heated is directly transferred to the colder current of gas and condensed there.

Some embodiments of my invention are illustrated in the drawings afl'ixed to my specification. My improved process may be carried through in the apparatus shown by way of example.

In the drawings:

Fig. 1 is a perspective view of a horizontal heat exchanger,

Fig. 2 is a cross-sectional view through a modification of this type of exchanger,

Fig. 3 is a view of apart of a vertical heat exchanger in longitudinal section,

Fig. 4 is a view of a modification of this type of exchanger in longitudinal section,

Fig. 5 is a view in an elevation, illustrating the application of my invention to a continuous absorption machine working with an inert gas, and

Fig. 6 is a diagrammatic illustration of air absorption machine embodying the principles of the invention.

Referring to Fig. 1 of the drawings 1 and 2 are pipes connected with each other by welding and arranged side by side one slightly above the other so that along the place of contact the heat carried by the gas current flowing in the pipe 1 in the direction of the arrow at passes to the gas current which traverses the pipe 2 in the direction of the arrow y. The pipes l and 2 may either be placed horizontal or they may be slightly inclined. The bottom portion of the higher pipe 1 is in communication with the bottom portion of the lower pipe 2 by spaced U-shaped pipes 3, 3', 3" and so on. These U-shaped pipes enable the passage of liquid from the pipe 1 into the pipe 2. Since they also form a liquid seal they prevent the passage of gas from one pipe into the other. Now assuming the construction just described is incorporated in a refrigerating system employing an-inert gas between the evaporator and the absorber, an exchange ofheat will take place in the following manner: Due to the low temperature of the gas current traversing the pipe 2 from the evaporator to the absorber the current of warmer gas traversing the pipe 1 from the absorber to the evaporator is. cooled down to such an extent that the condensiblc refrigerant vapors in it separate completely or partly in the form of a liquid which form drops and pass through the U-shaped tubes 3, 3, 3" and so on into the pipe 2. The current of gas in the pipe 2 has a comparatively low refrigerant vapor pressure due to its initially considerably lower temperature. The liquid entering the pipe 2 from the pipe'l consequently evaporates there into the current of gas. The heat necessary for this evaporation is derived from the pipe 1 in which-an equal quantity of heat had been set free by the condensation. It might also be said that the cooling effect required for the formation of the condensate in the pipe 1 is eifected'by the passage of that quantity of heat which must be transferred from the pipe 1 to the pipe 2 in order to evaporate in that pipe an equal quantity of liquid. By this means a large heat transfer is effected.

If the temperature difierence of the two gas currents and consequently the relative content of the hotter gas current in vapors capable of being condensed, is very great it might happen that not all the condensate in the pipe conducting the colder current of gas is evaporated. In this case the liquid which is not evaporated may be caused to return into the vessel from which the pipe 1 is fed with gas.

A heat exchange device in which the two pipes are horizontally and concentrically disposed is shown in Fig. 2 of the drawings. In this case the inner pipe 11 conducts the warm gas and the pipe 12 enveloping it, the colder current 01 gas. To enable the condensate formed in the pipe 11 to pass into the pipe 12, the pipe 11 is provided at its underside of fine wire gauze 13 covering about a quarter of its circumference and through which the condensate is able to drip into the pipe 12. currents only a very small pressure difierence exists the liquid suspended in the wire gauze or fine wire netting prevents the passage of gas from one pipe into the other due to its surface tension.

Figs. 3 and 4 of the drawings show other arrangements for providing for an exchange 'of heat between two currents of gas. In both of these figures the pipe conducting the cold gas is located within the pipe traversed by the warmer current of gas- Referring to Fig. 3 of the drawings it will be seen that the conduit for the colder gas current consists of a number of pieces of pipe 21 which in a manner not illustrated are'mounted on the inner wall of a single continuous pipe 22 forming the conduit for the warmer current of gas. Each piece of pipe 21 opens at the bottom into an annular dish or trough 23 the outer edge of which is slightly higher than the inner edge. The lower end of the piece of pipe 21 doesnot touch the bettom of the annular dish 23 but extends into it so far only that in conjunction with a liquid filling the dish it forms a liquid seal against the gases. If now the inner pipe is traversed by a colder and the'outer by a warmer current of gas charged with vapors capable of being condensed, the condensate formed in the outer pipe from the vapors first settles on the outer wall of the sections of pipe 21, passes into the annular dishes or cups 23 and finally overflows over the lower inner edge of the dishes into the interior of the inner gas pipe where' it evaporates instantaneously due to the low steam pressure prevailing there. The heat required for the evaporation is again supplied by the heat of condensation which has become liberated during the condensation or liquefaction of the vapors in the outer pipe.

In the modification illustrated in Fig. 4 the outer pipe 25 likewise designed to conduct the current of the warmer gas consists of a continuous pipe while the inner one conducting the colder current of gas consists of a series of funnel-shaped rings 26 so arranged one above the other thatany two adjacent rings in conjunction with the liquid in the lower ring form a liquid seal for the gases. Here also the inner edge of the ring is lower than the outer edge so that the condensate depositing at the outside of the rings is able to pass into the interior of the inner pipe and evaporate'while maintaining the liquid seals.

My invention is of particular importance for the heat exchange of such gas pipes which form part of the gas mixture circulation system of a continuous absorption machine. If, for instance, an inert gas is admixed with the gaseous working medium in the evaporator and absorber of such an absorption machine for the purpose of equalizing the pressure and if this inert gas is circulated through the absorber and the evaporator by any suitable means which need not be here described in detail, it is for thermal reasons frequently desirable that the current of hotter gas leaving the absorber and charged with the vapor of the solvent enter into heat exchange rela- Assuming that between the two gas tion with the gas current returning from the evaporator to the absorber. In this way heat and refrigerant or absorption liquid vapor are not carried along into the evaporator and, on the other hand, the gases entering the absorber are at a low temperature. t i

' In Fig. 5 of the drawings such a gas mixture circulation system of an absorption machine is shown, the remaining parts of this machine being omitted. Referring to this figure 31 is the evaporator, 32- the absorber, 33 the pipe leading from the absorber to the evaporator and conducting the humid-warm gas mixture and 34 the pipe which returns the gas mixture charged with gaseous working medium into the absorber. Along a considerable part of its length the pipe 33 is located within the pipe 34. The pipe 34 is slightly inclined downwardly from the evaporator 31 to the absorber 32. The part of the gas pipe 33 located within the pipe 34 is on its underside provided with U-shaped tubes 35. The condensate of the entrained refrigerant vapor'is able continuous absorption machine operating with an inert auxiliary gas is illustrated .in Fig. 6 of the drawings. The apparatus is equipped with two heat interchange devices according to my invention. The gaseous refrigerant, such as ammonia, developed from an absorption solution in an electrically heated generator or still 41 raises the weak solution in an ascending pipe 42 into the gas separator or rectifier 43.- From the separator a gas pipe 44 leads into the condenser 45 and the condensate flows through a U-shaped pipe 46, which together with an intermediate vessel 47 forms a pressure maintaining device, at the top into the evaporator 48 where it evaporates into an inert gas. From the lower part of the rectifier 43 a U-shaped pipe 49 leads to a second generator or boiler 50 which is adapted to be heated by the application of heat of a higher temperature and in which there is also contained an inert gas. The absorption solution here still further deprived of gas passes through a U-shaped pipe 51 into the absorber 52. This absorber is in communication with the evaporator 48 by gas pipes 53 and 54. The gas pipe 53 ascending from the upper part of the absorber 52 rises up to a point located above the gas mixture outlet point of the evaporator 48, makes a bend and enters the evaporator 48 at the bottom. The gas mixture pipe 54 coming from the evaporator and opening into the absorber 52 at the bottom is passed vertically through an expanded part 55 of the rising portion of the pipe 53. Within the expanded part '55 the pipe 54 is designed in a manner similar to that shown in either Figs. 3 or 4 so that the condensate precipitated on its outside, of the from the gas mixture passes through a connecting pipe 5'7, which at the same time represents a gas connection, into the upper part of a second I ly inclined. They may be constructed in a man-' ner similar to that illustrated in Fig. 1, that is provided with a device for the passage of the condensate formed in the higher pipe 61 into the pipe 60. The gas mixture circulation in the system formed by the vessels 50 and 58 as well as by the gas pipes 60 and 61 is maintained by gaseous refrigerant supplied by a nozzle 62 opening into the gas pipe 61 and coming from the pipe 44. Any pressure gradient between the two gas mixture circulation systems is equalized by the gas pipe 57.

In the operation of the above described absorption machine a heat exchange first takes place between the currents of gas traversing the pipes 53 and 54 in the direction of the arrows shown in the drawings. The vapors of the solvent carried along in the pipe 53 are then condensed and the condensate is passed into the pipe 54 where it evaporates. The vapors conducted away from absorber 52 are thus returned to it while only a precooled and dried gas mixture enters the evaporator 48. In a very similar manner the heat exchange and the passage of the condensate takes place between the parts of the gas mixture pipes 60 and 61 in contact with each other and connecting the generator or boiler 50 with the absorber 58. Here also the inert gas charged with the vapors of the solvent traversing the pipe 61 in the direction of the arrow gives off to the gas current traversing the pipe 60 in the opposite direction not only part of its heat but also the condensate of the vapors condensed in it. In the pipe 60 the condensate evaporates upon absorption of the heat of condensation liberated during the condensation. Any part not evaporated is able to drain into the lower part ofthe boiler 50 owing to the inclination of the gas pipe 60 leading to this boiler- I claim as my invention:

1. In a heat exchange device for carrying out the heat exchange process specified, two gas pipes one located within the other for conducting the two currents of gas standing in heat exchange with each other, the bottom of the wall of the inner gas pipe consisting of a sieve-like structure, such as fine wire gauze.

2. In a heat exchange device for carrying out the heat exchange process specified, two vertical gas pipes one located within the other, the inner pipe constructed of pipe sections so joined that the condensate precipitated at the outside of their Walls is able to pass at the joints through a flow of liquid from one pipe to another while preventing the flow of gas from one pipe to another and means for transferring heat by conduction from gas in one pipe to liquid in another to thereby cause said liquid to evaporate, said last mentioned means including the walls of said pipes and a weld integrally uniting the same.

4. In a heat exchanger suitable for use in an absorption refrigerating apparatus two pipes adapted to conduct fluids into heat exchange relation with each other, means providing for the flow of liquid from one pipe to another while preventing the flow of gas from one pipe to another and means for transferring heat by conduction from gas in one pipe to liquid in another to thereby cause said liquid to evaporate, said last mentioned means comprising a fine mesh screen forming the bottom portion of one of said pipes and being located within the other of said pipes. 5. In a heat exchanger suitable for use in an absorption refrigerating apparatus two pipes adapted to conduct fluids into heat exchange relation with each other, means providing for the flow of liquid from one pipe to another while preventing the flow of gas from one pipe to another and means for transferring heat by conduction from gas in one pipe to liquid in another to thereby cause said liquid to evaporate, said last mentioned means including the walls of one of said pipes and cups for holding the liquid to be evaporated.

6. In a heat exchanger suitable for use in an absorption refrigerating apparatus two pipes adapted to conduct fluids into heat exchange relation with each other, means providing for the flow of liquid from one pipe to another While preventing the flow of gas from one pipe to another and means for transferring heat by conduction from gas in one pipe to liquid in another to thereby cause said liquid to evaporate, said last mentioned means including depending tubes connected to one pipe and disposed in thermal contact with liquid in the other pipe.

'7. In an apparatus suitable for use in an absorption refrigerating system a warm gas conduit and a cold gas conduit in heat exchange relation with each other, means for conducting liquidfrom the warm gas conduit to the cold gas conduit while preventing the flow of gases from one conduit to the other, means for supplying a warm gas laden with a condensible fluid to the warm gas conduit, means for supplying a cold gas to the cold gas conduit, the arrangement of said conduits and said liquid conducting means being suchthat as the warm gas in the warm gas conduit gives up heat to the cold gas in the cold gas conduit, the condensible fluid in the warm gas will condense and flow through said liquid conducting means into said cold gas conduit and thus into the presence of the cold gas therein, the arrangement of said conduits and said liquid conducting means also being 'such that the condensed fluid in the cold gas conduit is maintained at a higher temperature than the cold gas therein by the direct transferof heat from the warm gas in the warm gas conduit to the condensed fluid in the cold gas conduit, independently of, and in addition to the transfer of heat from the warm gas to thecold gas, to thereby cause the condensible fluid in the cold gas conduit to evaporate into the cold gas therein.

8. A process for transferring heat from a warm gas laden with a condensible fluid to 'a cold gas which comprises the steps of transferring a quantity of heat from the warm gas to the cold gas thereby lowering the temperature of the warm gas and causing the condensible fluid to condense, transferring the condensed fluid into the presence of the cold gas, transferringanother quantity of heat directly from the warm gas to having'means on one end forming a. liquid retaining means and means on the other end adapted to cooperate with the liquid retaining means of an adjacent section to provide a liquid seal device capable of conveying liquid between the inside and outside of said conduit while preventing the flow of gas through said seal device provided the pressure on the inside of said conduit is substantially the same as that on the outside thereof.

EDMUND ALTENKmCH.

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